The present invention relates to a method and an apparatus for growing a layer on one surface of a wafer, and especially to a method and an apparatus for growing a layer on one surface of a wafer by liquid phase deposition.
In the field of manufacturing integrated circuit (IC) and semiconductor device, the technique of forming a layer on a wafer is very important. The layer can be used as a gate oxide layer of metal-oxide-semiconductor (MOS), a field oxide layer for trench-isolating other devices, a mask for ion implantation and diffusion, a capping layer for preventing dopants from diffusing out, or a passivation layer for protecting a device from being scratched by dirt. There are many methods for growing a layer on the wafer, e.g. thermal oxidation, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), and electron cyclotron resonance chemical vapor deposition (ECRCVD). Both of the gate oxide and field oxide have to be made by the thermal oxidation because only the thermal oxidation can provide a oxide layer with a low interface trap density. However, technologically speaking, every method has its own limitation in usage. For the thermal oxidation, the required high temperature (700xcx9c1200xc2x0 C.) will easily deform the chip and destroy the structure (because of the redistribution of the dopants). The main drawbacks of the CVD method are the expensive equipment and the requirement of precisely-controlled temperature for forming a layer. As for other methods, they need not only the expensive equipment but a growing temperature over 300xc2x0 C. and are also more complex.
The liquid phase deposition (LPD) method is a new method for growing oxide layers. The growing temperature of this method is low (about 40xc2x0 C.) and the equipment is relatively cheap. Therefore, the LPD method is very useful for manufacturing the integrated circuit and the semiconductor device. However, no specific technique or process is needed for producing a great number of wafers, each of which has a LPD layer thereon. Like other methods, the LPD method has a problem that the layer will grow on both surfaces of a wafer. The process of etching the LPD layer on the back of a wafer is necessary after the layer is grown. If there is an apparatus and a method that can control the growth of the LPD layer only on one surface of a wafer, the cost and time of growing LPD layer on the back will be saved, and the process of etching the LPD layer on the back, of course, will be needless.
Therefore, the present invention provides a method and an apparatus for growing a layer on one surface of a wafer by the LPD method. The apparatus of the present invention is low-cost and the method of the present invention is relatively simple and effective. The present invention makes the LPD method more useful.
An object of the present invention is to provide a method for growing a layer on one surface of a wafer by the LPD method. At first, a first wafer is putted on a first wafer-holder by its first surface. Then, a growth-liquid vessel having a first opening at the bottom is mounted on the first wafer-holder by the first opening so that the first wafer on the first wafer-holder is in contact with the growth-liquid vessel. Thereafter, growth liquid is poured into the growth-liquid vessel to expose a second surface of the first wafer to the growth liquid for growing the layer on the second surface of the first wafer. Then, the first wafer is taken out from the first wafer-holder to obtain a wafer with a layer grown only on one surface. Therefore, this method can save a lot of money and time without etching the LPD layer on the back. This method is very effective.
Before the first opening of the growth-liquid vessel is mounted on the first wafer-holder, the method further includes a step of putting a first O-ring on the first wafer on the first wafer-holder. The O-ring can ensure that the first opening is well sealed with the first wafer-holder and no liquid will flow out. The O-ring has a diameter a little larger than that of the first opening and has a shape similar to that of the first wafer.
Preferably, after the growth liquid is poured into the growth-liquid vessel, the method further includes the steps of putting a second wafer on a second wafer-holder by its first surface and mounting the second wafer-holder on a second opening at the top of the growth-liquid vessel. The second wafer on the second wafer-holder is in contact with the growth-liquid vessel. Because the second wafer and the second wafer-holder are provided, the step of taking out the first wafer further includes more steps. At first, the growth-liquid vessel is inverted to let the first opening at the top thereof and the second opening at the bottom thereof to expose a second surface of the second wafer to the growth liquid. Then, the first wafer-holder is removed from the first opening of the growth-liquid vessel and the first wafer is removed from the first wafer-holder.
The method of the present invention can also be used to produce a plurality of wafers, each of which has a layer on one surface. A plurality of wafers are putted on the first and second wafer-holders with a space between each other to ensure that layers can be grown freely on the wafers. A plurality of growth-liquid vessels are mounted between them and each wafer is in contact with a corresponding growth-liquid vessel.
Another object of the present invention is to provide an apparatus for growing a layer on one surface of a wafer by the LPD method. The apparatus includes a growth-liquid vessel having a first opening at the bottom thereof for containing a growth liquid therein and a first wafer-holder for putting thereon a first wafer by a first surface. The first opening of the growth-liquid vessel is mounted on the first wafer-holder and the first wafer is in contact with the growth-liquid vessel so that a second surface of the first wafer is exposed to the growth liquid for growing the layer on the second surface of the first wafers. The combination of the growth-liquid vessel and the wafer-holder has a smaller volume and this apparatus is relatively simple and cheap.
According to the present invention, both of the growth-liquid vessel and the first wafer holder are made of an anti-corrosive material. The anticorrosive material is preferably polybutafluoroethylene (TEFLON) or polyethylene (PE).
The apparatus further includes a second wafer-holder mounted on a second opening of the growth-liquid vessel. The apparatus of the present invention can also be used to produce a plurality of wafers, each of which has a layer on one surface.